'93 silverado lift kit

Keep tires narrow and with a smooth tread if you want best possible MPG as those meaty looking aggressive treads consume more fuel as does increased width. MPG will suffer regardless because you will also be increasing the areodynamic drag of vehical too with lifting it. One other facteor will be axle ratios because when you lift it and install oversized tires the engine has to work hard and at a lower RPM at same road speed because the overall effective ratio is changed and it has more drag to overcome too now and this can hurt MPG a lot at times. No free lunches here but if you are serious and regear truck to match lift and tire size and use a smooth narrow tread you will minimize the effect of lift on MPG and overall performance. There are those that will tell you that bigger tires reduce RPM's and therefore save fuel but this is not true because your vehical does not operate in a vacum with no areodynamic drag or increased drag from tires. Below is a link to a tire size/axle ratio calculator that helps a lot here when trying to "sort" thing out on tires size and axle ratios